Correct Answer: Algae and blue-green algae

Solution : The correct option is Algae and blue-green algae.

Biofertilizers are organic fertilisers containing live microorganisms such as bacteria, fungus, or algae that can improve soil fertility and plant development. These microorganisms like algae and blue-green algae (cyanobacteria), may fix atmospheric nitrogen into a form that plants can utilise as a fertiliser. They are very beneficial in boosting the nitrogen content of the soil, which is required for plant growth. Compost and cattle dung, on the other hand, are organic products that can enhance soil structure and offer nutrients to plants; but, because they do not include living microorganisms, they are not classified as biofertilizers. Ammonium sulphate is a synthetic fertiliser that nourishes plants with nitrogen and sulphur, but it contains no live microbes and is not biofertilizer.